Apparatus for preparing biodegradable microparticle formulations containing pharmaceutically active agents

ABSTRACT

This invention is directed to an apparatus and method for producing microparticles comprising pharmacologically active agents and biodegradable polymers. The apparatus includes a spinning disk containing a reservoir in the center thereof and a flat inclined surface. The apparatus optionally includes serrations and/or a flat surface beneath the periphery of the disk that is parallel to the rotational axis of the disk. The invention is also directed to a method for producing microparticles containing pharmacologically active agents, using the spinning disk apparatus. Formulations containing ophthalmically active agents are provided. Formulations exhibiting zero order release rates are also described.

FIELD OF THE INVENTION

The present invention relates to the sustained release ofpharmaceutically (i.e., pharmacologically) active agents. The inventionspecifically relates to a method and apparatus for making microcapsulesand microspheres containing pharmaceutically active agents, especiallyophthalmic active agents.

BACKGROUND OF THE INVENTION

Pharmacologically active agents may be administered systemically, suchas orally or intravenously, or locally, such as topically orsubcutaneously. In either instance, it is often desirable to deliver tothe targeted location a dosage of these agents that is no greater thanthat which may be metabolized immediately, as dosages in excess thereofmay be unusable and/or harmful. This has traditionally requiredadministration of the agents at regular time intervals, which can belaborious and/or impractical and can also lead to errors inadministration.

As an alternative, pharmacologically active agent delivery systems havebeen developed whereby the active agent is delivered (preferably in aconsistent, sustained-release amount) over a period of time.Specifically with regard to locally administered agents,sustained-release has been accomplished by utilizing microparticlescontaining the active agent and one or more pharmacologically inactivematerials. Microparticles can be divided into “microspheres” and“microcapsules,” which are different from each other. Microspheresusually refer to a monolithic type formulation in which the drugmolecules are dispersed throughout a polymeric matrix. On the otherhand, microcapsules refer to reservoir devices in which the drug core issurrounded by a continuous polymeric layer or shell. The drug core of amicrocapsule may comprise the drug itself or a microsphere containingthe drug.

The microparticles are delivered to the desired location and the activeagent is released therefrom over an extended period of time. For ocularapplications, the microparticles can be delivered, for example, byinjection to the posterior segment of the eye using a designed cannula,or otherwise introduced as implants.

Release of the active agent from microspheres may involve melting,salvation, and/or biodegradation of the polymer matrix. In the case ofmicrocapsules, the active agent must penetrate the shell to reach thetarget location. This may be accomplished by mechanical rupture,melting, dissolution, ablation, and/or biodegradation of the shelland/or diffusion of the active agent through the shell.

In particular, biodegradable materials, such as polymers, that form amatrix with and/or encapsulate the pharmaceutically active agents, canbe employed as a sustained delivery system. By biodegradable, it ismeant that the materials are degraded or broken down under physiologicalconditions in the body such that the degradation products are excretableor absorbable by the body. The use of biodegradable polymers can providea sustained release of an active agent by utilizing the biodegradabilityof the polymer to control the release of the active agent therebyproviding a more consistent, sustained level of delivery.

The prior art discloses several methods of producing microparticles,including by solvent extraction, low-temperature casting, coacervation,hot melting, interfacial cross-linking, interfacial polymerization,spray drying, supercritical fluid expansion, supercritical fluidantisolvent crystallization, and solvent evaporation. Solvent extractioninvolves the use of organic solvents to dissolve water-insolublepolymers. A drug in soluble or dispersed form is added to the polymersolution, and the mixture is then emulsified in an aqueous phasecontaining a surface-active agent. The organic solvent diffuses into thewater phase facilitating precipitation of solid polymer microspheres. Anexample of this technology may be found in U.S. Pat. No. 4,389,330(issued to Tice, et al.).

A process known as low-temperature casting has been utilized to producemicroparticles. In this process, which is described in U.S. Pat. No.5,019,400 (issued to Gombotz, et al.), a polymer is dissolved in asolvent together with an active agent that can be either dissolved inthe solvent or dispersed in the solvent in the form of microparticles.The polymer/active agent mixture is atomized into a vessel containing aliquid non-solvent, and overlayed with a liquefied gas, at a temperaturebelow the freezing point of the polymer/active agent solution. The coldliquefied gas or liquid immediately freezes the polymer droplets. As thedroplets and non-solvent for the polymer are warmed, the solvent in thedroplets thaws and is extracted into the non-solvent, resulting inhardened microspheres.

Coacervation is based on salting out or phase separation from ahomogeneous polymer solution of hydrophilic polymers into small dropletsof a polymer-rich, second liquid phase. When an aqueous polymer solutionis partially dehydrated or desolvated by adding a strongly hydrophilicsubstance or a water-miscible, non-solvent, the water-soluble polymer isconcentrated in water to form the polymer-rich phase. This is known as“simple” coacervation. If water-insoluble drug particles are present asa suspension or as an emulsion, the polymer-rich phase is formed on thedrug particle surface to form a capsule under suitable conditions. In“complex” coacervation, the polymer-rich complex (coacervate) phase isinduced by interaction between two dispersed hydrophilic polymers(colloids) of opposite electric charges. This process is described innumerous patents, including U.S. Pat. No. 2,800,457 (issued to Green, etal.).

A hot melt or congealing process has been described wherein an activeagent is mixed with a polymer, which is melted at high temperatures. Theadmixture is then transferred to a centrifugal atomizer and the formeddroplets cooled and collected. This process is described in U.S. Pat.No. 3,080,293 (issued to Koff). Alternatively, as described in U.S. Pat.No. 4,898,734 (issued to Mathiowitz, et al.), the active agent is mixedwith the melted polymer, and the molten mixture is suspended in anon-miscible solvent, heated above the melting point of the polymer, andstirred continuously. Once the emulsion is stabilized, it is cooleduntil the core material solidifies.

Interfacial cross-linking may be employed if the polymer possessesfunctional groups that can be cross-linked by ions or multi-functionalmolecules. As described in U.S. Pat. No. 4,138,362, (issued toVassiliades, et al.), for example, producing microparticles byinterfacial cross-linking involves mixing a water-immiscible, oilymaterial containing an oil-soluble, polyfunctional cross-linking agent,and an aqueous solution of a polymeric emulsifying agent. Anoil-in-water emulsion is formed containing the polyfunctionalcross-linking agent dispersed in the form of microscopic emulsiondroplets in the aqueous continuous phase containing the emulsifyingagent, and a solid capsule wall is formed by the cross-linking of theemulsifying agent by the polyfunctional cross-linking agent.

Interfacial polymerization requires monomers that can be polymerized atthe interface of two immiscible substances to form a membrane. U.S. Pat.No. 4,119,565 (issued to Baatz, et al.) discloses a process forencapsulation wherein a poly-functional compound is dissolved in a corematerial, or in an inert solvent or solvent mixture, and subsequentlymixed with the core material. This homogeneous mixture is thenintroduced into a liquid phase immiscible therewith, for example water,which contains a material that catalyzes polymerization of thepoly-functional compound.

Another known microparticle process is spray drying, wherein a solidforming material, such as a polymer, which is intended to form the bulkof the particle, is dissolved in an appropriate solvent to form asolution. Alternatively, the material can be suspended or emulsified ina non-solvent to form a suspension or emulsion. An active agent is thenadded and the solution is atomized to form a fine mist of droplets. Thedroplets then enter a drying chamber where they contact a drying gas.The solvent is evaporated from the droplets into the drying gas tosolidify the droplets, thereby forming particles. The particles are thenseparated from the drying gas and collected. This process is describedin U.S. Pat. No. 6,308,434 (issued to Chickering, III, et al.), andreferences disclosed therein.

Microparticle formation using supercritical fluid expansion involves therapid dissolving of a solid material into a supercritical fluid solutionat an elevated pressure and then rapidly expanding the solution into aregion of relatively low pressure. This produces a molecular spray thatis discharged into a collection chamber. The solvent is vaporized andpumped away, and the particles are collected. An example of this processis described in U.S. Pat. No. 4,734,451 (issued to Smith).

Supercritical antisolvent crystallization, as disclosed in U.S. Pat. No.6,461,642 (issued to Bisrat, et al.), involves dissolving the activeagent, and, optionally, one or more carrier materials in a firstsolvent, introducing the solution and a supercritical or subcriticalfluid into an apparatus, wherein the fluid contains an anti-solvent(such as carbon dioxide) and a second solvent. The essentiallycrystalline particles formed contain the active agent in a solvatedform. The particles may be further dried using a dry anti-solvent in asupercritical or subcritical state.

One widely utilized process employs solvent evaporation to formmicroparticles containing active agents. In a solvent evaporationprocess, the active agent and matrix material are dissolved in avolatile organic solvent that is ultimately removed by raising thetemperature and/or lowering the pressure. The most widely utilizedapparatus for forming microparticles via solvent evaporationincorporates a rotating device, often referred to as a spinning disk.The spinning disk process was originally described in U.S. Pat. No.3,015,128, (issued on Jan. 2, 1962 to G. R. Somerville, Jr.), thedisclosure of which that is germane to the spinning disk process ishereby incorporated by reference in its entirety to the extent notinconsistent with the disclosures in this Application.

Since the advent of the spinning disk technology, numerous modificationsof the method and apparatus have been introduced; however, variousproblems associated therewith have not been alleviated. For example,broad particle size distributions are often obtained. Importantly, thenarrower the particle size distribution, the more calculable andrepeatable the dosage of active agents. In addition, “pure” coatingmaterial particles (placebo particles) are produced. This results indosage dilution if the placebo particles are administered, or additionalmanufacturing costs if the placebo particles have to be separated fromthe active agent-containing microparticles. Furthermore, agglomerationof microparticles occurs, which further affects particle sizedistribution. What is needed is an apparatus and method for producingmicroparticles having narrow particle size distribution, reduced placeboformation, decreased agglomeration of particles, and improved productyield.

SUMMARY OF THE INVENTION

A spinning disk apparatus for producing microparticles having thesedesired properties is provided wherein the apparatus contains asubstantially circular spinning disk comprising a substantially smoothannular disk surface comprising a substantially flat incline, wherein anouter peripheral edge thereof defines a first diameter and an innerperipheral edge thereof defines a second diameter, and wherein the areacircumscribed by the inner peripheral edge includes a reservoircomprising a top portion thereof defined by the inner peripheral edge ofthe annular disk surface, and wherein the reservoir is partially definedby a third diameter, located between the bottom of the reservoir and thetop portion of the reservoir, wherein the third diameter is greater thanthe second diameter. The spinning disk apparatus may comprise asubstantially flat surface beneath the annular disk surface andproximate the outer peripheral edge thereof, wherein the substantiallyflat surface lies in a plane that is substantially parallel to therotational axis of the spinning disk. In addition, the outer peripheraledge of the annular disk surface may comprise serrations.

A method for producing microparticles utilizing the above-describedspinning disk apparatus is provided. In an embodiment thereof,microspheres are produced by combining an active agent with a matrixmaterial to form a composition that is introduced to the reservoir ofthe spinning disk apparatus, and operating the apparatus to producemicrospheres comprising the active agent and the matrix material. Inanother embodiment thereof, a method for producing microcapsules is alsoprovided wherein microspheres are combined with a coating material andintroduced to the reservoir of the spinning disk apparatus and operationthereof produces microcapsules comprising the microspheres coated withthe coating material. The active agent may comprise a pharmacologicallyactive agent and the matrix and coating materials may comprisebiodegradable polymers.

Formulations comprising microparticles containing biodegradable polymersand an ophthalmically active agent are also provided. The ophthalmicallyactive agent may comprise anecortave acetate; an alcohol form thereof,derivatives thereof, and combinations thereof. In an embodiment, theformulation comprises microspheres containing the ophthalmically activeagent. In another embodiment, the formulation comprises microcapsulescontaining the ophthalmically active agent.

Formulations comprising microcapsules that when introduced to a livingorganism release a pharmacologically active agent at a substantiallyzero order rate are provided. The microcapsules comprise microspherescomprising a biodegradable polymer and containing more than about 15 wt.% of a pharmacologically active agent, and a biodegradable polymercoating material. In one aspect, the release of the pharmacologicallyactive agent at a substantially zero order rate extends over a timeperiod of at least about four weeks.

Microcapsules prepared by the methods described above are providedwherein the microcapsules, when introduced to a living organism, releasea pharmacologically active agent at a substantially zero order rate.These microcapsules comprise a biodegradable polymer coating materialover a microsphere core that comprises a biodegradable polymer and apharmacologically active agent. The microsphere contains more than about15 wt. % of the pharmacologically active agent. In one aspect, therelease of the pharmacologically active agent at a substantially zeroorder rate extends over a time period of at least about four weeks.

BRIEF DESCRIPTIONS OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates schematically a spinning disk apparatus in accordancewith an embodiment of the present invention;

FIG. 2 illustrates schematically a spinning disk in accordance withprior art technology;

FIG. 3 illustrates schematically a spinning disk in accordance withprior art technology;

FIG. 4A illustrates schematically a spinning disk in accordance withprior art technology;

FIG. 4B illustrates schematically a spinning disk in accordance withprior art technology;

FIG. 4C illustrates schematically a spinning disk in accordance withprior art technology;

FIG. 5 illustrates schematically a spinning disk in accordance withprior art technology;

FIG. 6 illustrates schematically a conventional spinning disk inaccordance with prior art technology;

FIG. 7 illustrates schematically a side view of a spinning disk inaccordance with an embodiment of the present invention;

FIG. 8 illustrates schematically a top view of one embodiment of thespinning disk depicted in FIG. 7;

FIG. 9 shows particle size distribution curves generated by comparing ahypothetical population of microparticles produced with the spinningdisk of the present invention and a conventional spinning disk;

FIG. 10 shows a magnified image at 50×magnification of microcapsulesproduced according to one embodiment of the present invention wherein areduced number of placebo particles are formed;

FIG. 11 shows a magnified image at 200×magnification of microcapsulesproduced according to one embodiment of the present invention whereinthe microcapsules manifest an improved coating uniformity;

FIG. 12 shows a magnified image at 50×magnification of microcapsulesproduced using a conventional spinning disk;

FIG. 13 shows another magnified image at 200×magnification ofmicrocapsules produced using a conventional spinning disk

FIG. 14 shows a graph depicting the amount of the active agent releasedover time from various microparticles produced by the present invention.

DETAILED DESCRIPTION

FIG. 1 depicts a spinning disk apparatus 100 in accordance with anembodiment of the present invention. Spinning disk apparatus 100includes a spinning disk 105, which is coupled to stirrer motor 115 byconnecting rod 120. Spinning disk 105 is typically substantiallycircular and can have a diameter of between about 10 mm and about 300mm. As will be described in greater detail below, spinning disk 105 mayhave a variety of surface features and comprise various geometries.Stirrer motor 115 is supported within spinning disk apparatus 100 by amotor mounting frame 125. Stirrer motor 115, which may be drivenhydraulically, pneumatically or electrically, is adapted to rotatespinning disk 105 via connecting rod 120. Stirrer motor 115 includes aspeed control system (not shown) adapted to rotate spinning disk 105 atvarious speeds, such as from about 60 rpm to about 25,000 rpm.

Spinning disk apparatus 100 also includes a sample delivery system 130,that includes one or more feed vessels 135, one or more fluid pumps 140,and a fluid delivery system 145. Fluid delivery system 145 typicallycomprises a tube through which the materials to be processed within diskapparatus 100 are introduced onto spinning disk 105. Fluid pumps 140 aretypically adapted to deliver fluids from feed vessels 135 to spinningdisk 105 via fluid delivery system 145 at flow rates of about 0 to about750 g/min. Feed vessels 135 include one or more agitation means 150(such as a stirrer) adapted to facilitate mixing of materials introducedinto feed vessels 135 and may optionally include a temperature controlsystem (not shown) adapted to control the temperature of materialscontained therein.

Proximate spinning disk 105 is a heating unit 155, which may be incontact with or integral to spinning disk 105 as shown, oralternatively, disposed in close, non-contacting proximity thereto.Suitable heating units 155 include, but are not limited to, capacitanceheaters, impedance heaters, liquid circulation heaters, hot air guns,and the like.

Spinning disk apparatus 100 includes a process chamber 160, whichhermetically seals a space surrounding spinning disk 105 and is operablyconnected to a gas source (not shown) adapted to maintain theenvironment within process chamber 160 under a controlled atmosphere.Process chamber 160 may optionally include a vacuum source (not shown)adapted to control the pressure within process chamber 160. The gaseousenvironment maintained within process chamber 160 may comprise air orsome inert gas or gases which are supplied to the process chamber 160 bya gas feed means (not shown). Process chamber 160 may comprise thermallycontrollable internal surfaces, comprising a material such as, but notlimited to, jacketed stainless steel. Alternatively or additionally,process chamber 160 may include internal surfaces having low thermalconductivity, such as, but not limited to, plastic. In one embodiment,the plastic utilized is high density polyethylene (HDPE), however, theinvention is not limited to this material and other similarly suitablematerials may be employed.

Process chamber 160 may include a cone bottom tank containing internalsurfaces comprising the abovementioned materials. Spinning diskapparatus 100 additionally can include a sample collection system 165,which is operably connected to process chamber 160. Suitable samplecollection systems 165 include, but are not limited to, cycloneseparators. Operably connected to sample collection system 165 may be anevacuation system 170, which can include one or more filters 175, one ormore blowers 180, one or more air flow control valves 185, and one ormore vents 190. A cyclone separator comprising sample collection systems165 may also comprise a thermally controllable internal surface, suchas, but not limited to, jacketed stainless steel, and/or surfaces havinglow thermal conductivity, such as, but not limited to, plastic. In oneembodiment, the plastic utilized is high density polyethylene (HDPE),however, the invention is not limited to this material and othersimilarly suitable materials may be employed.

In addition as will be described in more detail below, sample collectionsystem 165 may be run continuously. The surfaces of spinning diskapparatus 100 that contact the microparticles produced therein,including but not limited to, surfaces of process chamber 160 and samplecollection systems 165, may be thermally controlled by temperaturecontrol devices (not shown) to reduce particle agglomeration.

FIGS. 2-6 depict spinning disks in accordance with prior art technology.FIG. 2 shows a substantially flat spinning disk as disclosed in U.S.Pat. No. 3,015,128 (issued to Somerville, Jr.), with whichmicroparticles are produced by introducing materials through line 221onto the surface of 223 of spinning disk 215 proximate the centerthereof. Spinning disk 215 is rotated by drive shaft 217 using a motor(not shown) operably connected thereto, thereby urging the materialsintroduced onto the surface 223 of spinning disk 215 radially outwardlyalong the surface 223 to the peripheral edge 224 of spinning disk 215where the materials are trajected outwardly from random points andthereby separated into discrete particles 228.

FIG. 3 shows a prior art spinning disk containing teeth around theperiphery thereof, as disclosed in U.S. Pat. No. 4,256,677 (issued toLee). As depicted therein, the materials fed through outlet 317 onto thesurface of rotating disk 321 which contains teeth 320 around theperiphery thereof. Outlet 317 is disposed such that the materialsintroduced thereby contact the surface of toothed disk 321 near theperiphery thereof. Toothed disk 321 is convex with respect to theintroduction of materials via outlet 317 and is heated using heatingelement 324 disposed proximate the peripheral edge of toothed disk 321.Using conventional spinning disk methodology as previously described,microparticles are thereby produced.

FIGS. 4A-4C depict prior art spinning disks having a concave geometry,as disclosed in U.S. Pat. No. 4,675,140 (issued to Sparks, et al.). FIG.4A shows an angled spinning disk 490, onto which is introduced molten ordissolved coating material 421 and core material 427, which may comprisea solid particles or liquid droplets. Using conventional spinning diskmethodology as previously described, microparticles comprising coreparticles 427 with a liquid coating layer 427 a, and droplets 421 a ofexcess unused coating material 421, are thereby produced. FIG. 4B showsa parabolic spinning disk 492 and FIG. 4C shows a sigmoidal spinningdisk 494, which form microparticles as described above.

FIG. 5 shows a prior art spinning apparatus having a cup-shapedrotational member, as disclosed in U.S. Pat. No. 5,643,594 (issued toDorian, et al.). As described therein, the cup 512 receives a supplymixture 518 of a suspension of particles in a solution of a coatingpolymer, via a conduit or tube 519. The cup 512 includes a mixingchamber 520, which extends into an upwardly diverging, conically shapedsidewall 522, and which terminates into an upper rim or edge 525. Thecup 512 is designed to project the beads 514 radially outwardly along agenerally horizontal trajectory by employing conventional spinning diskmethodology as previously described.

FIG. 6 shows a conventional prior art spinning apparatus (“conventionaldisk”) as described in Johnson, D. E., et. al, “A New Method for CoatingGlass Beads for Use In Gas Chromatography of Chloropromazine and ItsMetabolites,” J. Gas Chrom., 3, 345-47 (1965), the disclosure of whichthat is germane to the spinning disk is hereby incorporated by referencein its entirety to the extent not inconsistent with the disclosures inthis Application. The conventional disk depicted therein includes aconcave geometry in which the disk surface curves sigmoidally from thecenter to the periphery thereof. For purposes of generally disclosingfeatures and advantages of the present invention as discussed below, theconventional disk described in the above cited reference constitutes thestandard for comparison.

FIG. 7 depicts a spinning disk encompassing one embodiment of thepresent invention. Spinning disk 105 includes a substantially smoothannular surface 706 on what is defined herein as the top face ofspinning disk 105. Spinning disk 105 comprises an outer peripheral edge707. Spinning disk 105 also includes a reservoir 708 partially definedby an inner peripheral edge 709 of spinning disk 105 and disposed in thecenter thereof. Reservoir 708 has a vertical displacement H₁ that can bebetween about 5 mm and about 20 mm. A diameter D₃ defines a maximumwidth of reservoir 708, while a diameter D₂ defines a minimum width ofreservoir 708. Diameter D₃ can be in the range of about 1 mm to about 20mm. Diameter D₂ can be in the range of about 1 mm to about 20 mm. Thediameter D₂ is disposed closer to the open end of reservoir 708 than isdiameter D₃. That is to say, reservoir 708 has an opening that isnarrower than at least some cross-sectional area below the opening. Thisgeometry produces a lip 710 at the top of reservoir 708.

Annular surface 706 has diameter D₁ that can be between about 10 mm toabout 300 mm. Annular surface 706 comprises a flat incline that definesa fixed angle α, which may range from about 2 degrees to about 85degrees, preferably from about 5 degrees to about 45 degrees, and morepreferably from about 15 degrees to about 30 degrees. An additionaloptional feature of spinning disk 105 is a substantially flat surface711 substantially parallel to the disk rotational axis beneath annularsurface 706 proximate outer peripheral edge 707. The substantially flatsurface 711 may range from about 1 mm to about 10 mm in length. Theinclusion of surface 711 having this geometry assists in more accuratelymachining disk 105 by providing a second reference surface to aid inre-fixturing and significantly reducing chatter during thedisk-machining process.

Spinning disk 105 may be composed of any suitable material that can befabricated to meet the specifications therefor, such as a metallic orsynthetic material. In certain embodiments spinning disk 105 wasfabricated from 304 or 316 stainless steel, however the presentinvention is not limited to disks comprising these materials. Annularsurface 706 and the surface of reservoir 708 may be ground and polishedto a mirror finish; however, one skilled in the art would understandthat the surface characteristics of a spinning disk affect theperformance thereof and may be optimized to achieve desired results.

As shown in FIG. 8, Spinning disk 105 may optionally include serrations(“teeth”) 712 comprising outer peripheral edge 707. Teeth 712 may definean angle β, which may range from about 145 degrees to about 10 degrees,preferably from about 105 degrees to about 15 degrees, and morepreferably from about 65 degrees to about 20 degrees. However, oneskilled in the art would understand that the angle β would affect theperformance of a spinning disk and could be optimized to achieve desiredresults. Teeth 712 may define a horizontal displacement D₄ of betweenabout 0 μm and about 5,000 μm.

The apparatus described in FIGS. 1, 7, and 8 may be employed to producemicroparticles in accordance with embodiments of the present invention.In one aspect, the apparatus is utilized to produce microspheres. In anembodiment, the microspheres are produced by dispersing apharmacologically active agent in solutions containing a biodegradablepolymer. Referring again to FIG. 1, the solution is prepared byintroducing a biodegradable polymer and a solvent to feed vessel 135.Suitable biodegradable polymers include, but are not limited to, polylactic acids, (PLA), poly glycolic acids (PGA), poly lactic-glycolicacids (PLGA), polycaprolactone (PCL), poly orthoesters, polyanhydrides,polyesters, cellulosics, triglycerides (such as Sterotex K and SterotexNF), poly ethylene glycols (PEG), and combinations thereof. Suitablesolvents include any material in which the biodegradable polymer willdissolve. Such solvents include, but are not limited to, methanol,ethanol, methylene chloride, chloroform, ethyl acetate, acetone, andcombinations thereof. Although less volatile solvents may be used inaccordance with the invention, it is a particular feature of the presentinvention that lower boiling solvents may be employed.

The pharmacologically active agent is thereupon dispersed in thebiodegradable polymer solution by introduction thereof into feed vessel135. Suitable pharmacologically active agents that may be used toadvantage with the present invention include, but are not limited to,ophthalmically active agents, angiogenic inhibitors, anti-inflammatoryagents (steroidal and non-steroidal), tyrosine kinase inhibitors,anti-infectives, (e.g., antibiotics, antivirals, and antifungals),anti-allergic agents (e.g., antihistamines and mast cell stabilizers),cyclooxygenase inhibitors, (e.g., Cox I and Cox II inhibitors),decongestants, anti-glaucoma agents, (e.g., adrenergics,.beta.-adrenergic blocking agents, alpha-adrenergic agonists,parasypathomimetic agents, cholinesterase inhibitors, carbonic anhydraseinhibitors, and prostaglandin analogs), phosphatidyl-inositol kinaseinhibitors, gama-aminobutyric acid and derivatives thereof (includingGabapentin and Pregabalin), antioxidants, nutritional supplements,agents for the treatment of cystoid macular edema (e.g., non-steroidalanti-inflammatory agents), agents for the treatment of age relatedmacular degeneration (ARMD), (e.g., angiogenesis inhibitors andnutritional supplements), agents for the treatment of herpeticinfections and cytomegalovirus (CMV) ocular infections, agents for thetreatment of proliferative vitreoretinopathy (e.g., antimetabolites andfibrinolytics), wound modulating agents (e.g., growth factors),anti-metabolites, neuroprotective drugs (e.g., eliprodil), angiostaticsteroids for the treatment of diseases or conditions of the posteriorsegment of the eye, (e.g., ARMD, choroidal neovascularization (CNV),retinopathies, retinitis, uveitis, macular edema, and glaucoma), andcombinations thereof. One specific pharmacologically active agentsuitable for employment with the present invention is the ophthmalicallyactive agent anecortave acetate(4,9(11)-pregnadien-17α,21-diol-3,20-dione-21-acetate), which may alsobe utilized in its alcohol form(4,9(11)-pregnadien-17α,21-diol-3,20-dione), or in other pro-drugderivative forms.

Once the dispersion or solution containing the pharmacologically activeagent, the biodegradable polymer, and the solvent is prepared, thedispersion is transferred to the top face of a rotating spinning disk105 using fluid pump 140 and fluid delivery system 145. While thedispersion may be introduced onto the spinning disk 105 on any portionthereof (including annular surface 706), it is a feature of the presentinvention that the dispersion may be introduced into reservoir 708.Prior to and throughout the microsphere manufacture, process chamber 160is maintained at conditions conducive to controlled evaporation of thesolvent from the dispersion. This is accomplished by controlling thetemperature of annular surface 706 and reservoir 708 (using heating unit155) and the temperature and/or pressure of the process chamber 160(using a vacuum source not shown) such that the evaporation rate of thesolvent enhances the production of microspheres. One skilled in the artwould appreciate the affects of temperature and pressure on solventevaporation (and, hence, microsphere production) and understand thatconditions may be optimized to produce the desired materials.

Upon introduction of the dispersion or solution into reservoir 708, thecentrifugal force transferred to the dispersion from rotating spinningdisk 105 urges the dispersion as a liquid film up the interior surfaceof reservoir 708. Prior to the liquid film advancing outward onto theflat angled portion of annular surface 706 of spinning disk 105 towardthe outer peripheral edge 707, it must traverse the lip 710 of reservoir708. It is a feature of the present invention that the lip 710 isdisposed between of reservoir 708 and the flat angled portion of annularsurface 706 extending to the outer peripheral edge 707. Once the liquidfilm has propagated beyond lip 710, the dispersion becomes more viscousas the solvent is evaporatively removed therefrom. It would beunderstood by one skilled in the art that the rotation speed of spinningdisk 105, in contemplation of the composition of the dispersion and theenvironmental conditions of process chamber 160, may be optimized toachieve the desired microsphere production.

The materials in the dispersion or solution can be atomized by beingrotatively urged beyond the outer peripheral edge 707 and controllablyejected from the edge of spinning disk 105. Solidification of theatomized material as it falls to the bottom of process chamber 160results in the formation of microspheres comprising thepharmacologically active agent and the biodegradable polymer. Themicrospheres so produced are collected using sample collection system165. Microspheres having a diameter of about 1 μm to about 2,500 μm maybe produced by this process. The microspheres so produced may compriseabout 0.0001 wt. % to about 99 wt. % active agent, preferably about0.001 wt. % to about 55 wt. % active agent, and more preferably about0.01 wt. % to about 30 wt. % active agent.

In another embodiment of the present invention, microspheres areproduced using a hot melt process (as generally described in U.S. Pat.No. 3,080,293 (issued to Koff)) that employs the apparatus of thepresent invention. In this embodiment, the biodegradable polymer isintroduced to feed vessel 135 and melted or partially melted therein.Once the biodegradable polymer exists in the desired molten or partiallymolten state, the pharmacologically active agent is introduced thereto.As previously described, the dispersion can then be introduced to thereservoir 708 of rotating spinning disk 105 via fluid delivery system145. The centrifugal force urges the dispersion as a liquid film up theinterior surface of reservoir 708 and beyond the lip 710 of reservoir708. The dispersion can be maintained in a molten or partially moltenstate by the temperature of annular surface 706 as it propagates outwardto outer peripheral edge 707. The dispersion is rotatively ejected fromspinning disk 105 and congeals as microspheres as it falls to the bottomof process chamber 160. The microspheres so produced can be collectedusing sample collection system 165. Microspheres having a diameter ofabout 1 μm to about 2,500 μm may be produced by this process. Themicrospheres so produced may comprise about 0.0001 wt. % to about 75 wt.% active agent, preferably about 0.001 wt. % to about 45 wt. % activeagent, and more preferably about 0.01 wt. % to about 30 wt. % activeagent.

In additional embodiments of the present invention, microspheres may beproduced comprising core materials other than pharmacologically activeagents. Thus, the apparatus of the present invention may be employed toproduce microspheres suitable for introduction into living organismswherein the sustained release materials do not cause pharmacologic orpathologic responses in vivo. Examples of such materials include, butare not limited to, dyes, radioactive compounds, imaging agents, quantumdots, contrast agents, and combinations thereof. Further, microspheresproduced according to the present invention may comprise agents that aredesigned to be non-physiologically active ex vivo. Examples include, butare not limited to, ultraviolet blocking or absorbing compounds,deodorants or antiperspirants, emollients, cosmetics, and combinationsthereof. In addition, microspheres produced according to the presentinvention may comprise matrix materials other than biodegradablepolymers. Suitable materials include, but are not limited to, waxes,lipids, oils, gums, resins, cellulose, starches, non-biodegradablepolymers, and combinations thereof.

In another aspect of the present invention, microcapsules comprising acoated microsphere can be produced. The formation of microcapsulesinvolves applying an over-coat to microspheres utilizing the apparatusof the present invention. In an embodiment, microcapsule productionaccording to the present invention involves applying a biodegradableover-coat to microspheres comprising a pharmacologically active agentand biodegradable polymer matrix. In this embodiment, a solutioncomprising a coating material and a solvent can be prepared in feedvessel 135. Suitable solvents include any material in which the coatingmaterial will dissolve but in which the microspheres are substantiallyinsoluble. Such solvents include, but are not limited to, methanol,ethanol, methylene chloride, chloroform, ethyl acetate, acetone, andcombinations thereof. Although less volatile solvents may be used inaccordance with the invention, it is a feature of the present inventionthat lower boiling solvents may be employed. It is also a feature ofthis invention that the solvent utilized for microcapsule formation maybe one incapable of extracting significant amounts of the active agentfrom the microsphere matrix. Suitable coating materials include, but arenot limited to, poly lactic acids, (PLA), poly glycolic acids (PGA),poly lactic-glycolic acids (PLGA), polycaprolactone (PCL), polyorthoesters, polyanhydrides, polyesters, cellulosics, triglycerides(such as Sterotex K and Sterotex NF), poly ethylene glycols (PEG), andcombinations thereof.

A microsphere comprising a pharmacologically active agent and abiodegradable polymer can be dispersed in the coating material solution.The dispersion thus formed can be introduced as previously describedwith reference to microsphere production into reservoir 708 of spinningdisk 105 via fluid delivery system 145. As described above, thecentrifugal force transferred to the dispersion from rotating spinningdisk 105 can urge the dispersion as a liquid film up the interiorsurface of reservoir 708 beyond the lip 710. As described above, oncethe liquid film has propagated beyond lip 710, the dispersion becomesmore viscous as the solvent is evaporatively removed therefrom. It wouldbe understood by one skilled in the art that the rotation speed ofspinning disk 105, in contemplation of the composition of the dispersionand the environmental conditions of process chamber 160, may beoptimized to achieve the desired microcapsule production.

The materials in the dispersion can be atomized by being rotativelyurged beyond outer peripheral edge 707 and ejected from spinning disk105. Solidification of the atomized material as it falls to the bottomof process chamber 160 results in the formation of microcapsulescomprising an outer layer of the biodegradable coating material over themicrosphere core. The microcapsules so produced can be collected usingsample collection system 165. Microcapsules having a diameter of about 1μm to about 2,500 μm may be produced by this process. Microcapsules soproduced have a coating comprised of about 0.002 vol. % to about 96 vol.%, preferably about 0.003 vol. % to about 50 vol. %, and more preferablyabout 0.004 vol. % to about 5 vol. %. The microcapsules so produced maycomprise about 0.0001 wt. % to about 99 wt. % active agent, preferablyabout 0.001 wt. % to about 50 wt. % active agent, and more preferablyabout 0.01 wt. % to about 30 wt. % active agent.

In an additional embodiment, microencapsulation utilizing the apparatusof the present invention may comprise a hot melt process. In thisembodiment, a biodegradable polymer coating material is introduced tofeed vessel 135 and melted or partially melted therein. Once the coatingmaterial exists in the desired molten or partially molten state, amicrosphere comprising a pharmacologically active agent and abiodegradable polymer is introduced thereto. As previously described,this dispersion is then introduced to the reservoir 708 of rotatingspinning disk 105 via fluid delivery system 145. The centrifugal forceurges the dispersion as a liquid film up the interior surface ofreservoir 708 and beyond the lip 710 of reservoir 708. The dispersion ismaintained in a molten or partially molten state by the temperature ofannular surface 706 as it propagates outward to outer peripheral edge707. The dispersion is rotatively ejected from spinning disk 105 andcongeals as microcapsules comprising an outer layer of the biodegradablecoating material over the microsphere core as it falls to the bottom ofprocess chamber 160. The microcapsules so produced are collected usingsample collection system 165. Microcapsules having a diameter of about 1μm to about 2,500 μm may be produced by this process. Microcapsules soproduced have a coating comprised of about 0.002 vol. % to about 96 vol.%. The microcapsules so produced may comprise about 0.0001 wt. % toabout 99 wt. % active agent, preferably about 0.001 wt. % to about 50wt. % active agent, and more preferably about 0.01 wt. % to about 30 wt.% active agent.

Embodiments of the present invention encompass microcapsule productionutilizing the apparatus described herein. Microspheres employed toproduce microcapsules according to the present invention may be producedusing the herein described apparatus as disclosed above, or produced byanother suitable process. In addition, microspheres encapsulatedaccording to the present invention may comprise active agents that arenon-pharmacologically active and/or matrix materials that do notcomprise biodegradable polymers, such as the microspheres previouslydescribed herein. In additional embodiments, microcapsule production maybe achieved in accordance with the present invention whereby the coatingmaterial does not comprise a biodegradable polymer. Suitable materialsinclude, but are not limited to, waxes, lipids, oils, gums, resins,cellulose, starches, non-biodegradable polymers, and combinationsthereof.

The following Examples are provided to demonstrate particularembodiments of the present invention. It should be appreciated by thoseof skill in the art that the methods disclosed in the Examples thatfollow merely represent exemplary embodiments of the present invention.However, those of skill in the art should, in light of the presentdisclosure, appreciate that many changes can be made in the specificembodiments described and still obtain a like or similar result withoutdeparting from the spirit and scope of the present invention.

EXAMPLE 1

In one embodiment of the microsphere manufacturing process describedabove, 312 g of an 8% poly lactide-co-glycolide (PLGA) 50:50 solution in60:40 acetone/methylene chloride was prepared in feed vessel 135. Tothis solution was added 9.7 g of anecortave acetate, and the resultingdispersion was transferred at a rate of about 120 g/min. via fluiddelivery system 145 into the reservoir 708 of a spinning disk 105 havinga diameter of about 76.2 mm, rotating at a rate of about 3,000-4,000rpm. Utilizing a process chamber 160 comprising an internal surface ofhigh-density polyethylene (HDPE), microspheres were formed byevaporative removal of the solvent with an outlet temperature of theprocess chamber 160 of about 48-50° C. An 88% yield (30.6 g) ofmicrospheres was collected as a free-flowing powder using a cycloneseparator.

COMPARATIVE EXAMPLE 1

In an example comparable to Example 1 above, a stainless steel processchamber 160 was used instead of the plastic, less thermally conductivematerial. Therein, 250 grams of an 8% poly lactide-co-glycolide (PLGA)50:50 solution in 60:40 acetone/methylene chloride was prepared in feedvessel 135. To this solution was added 7.8 g of anecortave acetate, andthe resulting dispersion was transferred at a rate of about 125 g/min.via fluid delivery system 145 into the reservoir 708 of a spinning disk105 having a diameter of about 76.2 mm, rotating at a rate of about3,000-4,000 rpm. The microspheres were formed by evaporative removal ofthe solvent with an outlet temperature of the stainless steel processchamber 160 of 48-50° C. The microspheres agglomerated on the sides ofstainless steel process chamber 160 and no discrete microspheres werecollected.

EXAMPLE 2

In an embodiment of the microsphere manufacturing process describedherein, 200 g of 5% poly lactide-co-glycolide (PLGA) 90:10 solution inacetone was prepared in feed vessel 135. To this solution was added 6.7g of anecortave acetate. The resulting dispersion was transferred at arate of about 180 g/min. via fluid delivery system 145 into thereservoir 708 of a spinning disk 105 having a diameter of about 76.2 mm,rotating at a rate of about 4,000-5,000 rpm. Utilizing a process chamber160 comprising an internal surface of high-density polyethylene (HDPE),the microspheres were formed by evaporative removal of the acetone withan outlet temperature of the process chamber 160 of about 45° C. A 90%yield (15.0 g) of microspheres was collected as a free-flowing powderusing a cyclone separator.

EXAMPLE 3

In an embodiment of the microsphere manufacturing process describedherein, 200 g of 5% poly lactide-co-glycolide (PLGA) 90:10 solution inacetone was prepared in feed vessel 135. To this solution was added 0.5g of polyethylene glycol (PEG 400) and 3.5 g of anecortave acetate. Theresulting dispersion was transferred at a rate of about 200 g/min. viafluid delivery system 145 into the reservoir 708 of a spinning disk 105having a diameter of about 76.2 mm, rotating at a rate of about4,000-5,000 rpm. Utilizing a process chamber 160 comprising an internalsurface of high-density polyethylene (HDPE), the microspheres wereformed by evaporative removal of the acetone with an outlet temperatureof the process chamber 160 of about 45° C. A 77% yield (10.8 g) ofmicrospheres was collected as a free-flowing powder using a cycloneseparator.

EXAMPLE 4

In an embodiment of the microsphere manufacturing process describedherein, 100 g of 5% poly lactide-co-glycolide (PLGA) 75:25 solution inacetone was prepared in feed vessel 135. To this solution was added 0.56g of Isopropyl(Z)-7-[(1R,2R,3R,5R)-5-chloro-3-hydroxy-2-[(3R)-[3-cyclohexyl-3-hydroxy]-1-propyl]cyclopentyl]-5-heptenoate.The resulting solution was transferred at a rate of about 85 g/min. viafluid delivery system 145 into the reservoir 708 of a spinning disk 105having a diameter of about 76.2 mm, rotating at a rate of about 5,500rpm. Utilizing a process chamber 160 comprising an internal surface ofhigh-density polyethylene (HDPE), the microspheres were formed byevaporative removal of the acetone with an outlet temperature of theprocess chamber 160 of about 45° C. A 56% yield (3.09 g) of microsphereswas collected as a free-flowing powder using a cyclone separator.

EXAMPLE 5

In an embodiment of the microsphere manufacturing process describedherein, 489 g of 4.5% poly lactide-co-glycolide (PLGA) 85:15 solution inacetone was prepared in feed vessel 135. To this solution was added0.396 g of 5-Fluorouridine (5-FUD). The resulting solution wastransferred at a rate of about 55 g/min via fluid delivery system 145into the reservoir 708 of a spinning disk 105 having a diameter of about76.2 mm, rotating at a rate of about 5,500 rpm. Utilizing a processchamber 160 comprising an internal surface of high-density polyethylene(HDPE), the microspheres were formed by evaporative removal of theacetone with an outlet temperature of the process chamber 160 of about45° C. A 70% yield (15.55 g) of microspheres was collected as afree-flowing powder using a cyclone separator.

EXAMPLE 6

In an embodiment of the microsphere manufacturing process describedherein, 100 g of 5% poly lactide-co-glycolide (PLGA) 75:25 solution in90:10 acetone/ethyl acetate was prepared in feed vessel 135. To thissolution was added 0.56 g of Isopropyl(Z)-7-[(1R,2R,3R,5S)-3,5-dihydroxy-2-[(1E,3R)-[3-hydroxy-4-[(α,α,α-trifluoro-m-tolyl)oxy]]-1-butenyl]cyclopentyl]-5-heptenoate.The resulting solution was transferred at a rate of about 71 g/min. viafluid delivery system 145 into the reservoir 708 of a spinning disk 105having a diameter of about 76.2 mm, rotating at a rate of about 5,500rpm. Utilizing a process chamber 160 comprising an internal surface ofhigh-density polyethylene (HDPE), the microspheres were formed byevaporative removal of the acetone with an outlet temperature of theprocess chamber 160 of about 46° C. A 68% yield (3.8 g) of microsphereswas collected as a free-flowing powder using a cyclone separator.

EXAMPLE 7

In an embodiment of the microcapsule manufacturing process describedherein, 42.7 g of a triglyceride (Sterotex NF, available from AbitecCorp., Janesville, Wis.) was melted in feed vessel 135 at a temperatureof about 90-95° C. To the molten material was added 15.0 g of anecortaveacetate, and the resulting dispersion was transferred at a rate of about50-60 g/min. via fluid delivery system 145 into the reservoir 708 of aspinning disk 105 having a diameter of about 76 mm, rotating at a rateof about 7,500-8,500 rpm. Spinning disk 105 was maintained at atemperature of about 90-100° C. Microspheres were formed by cooling ofthe hotmelt with an outlet temperature of the process chamber 160 ofabout 22-28° C. An 80% yield (46.5 g) of microspheres was collected as afree-flowing powder using a cyclone separator. An over-coat was appliedto a portion of the so produced microspheres. This was accomplished bypreparing 100 g of a 5% solution of poly lactide-co-glycolide (PLGA)75:25 in 60:40 acetone/ethyl acetate in feed vessel 135 and thendispersing therein 20.0 g of the microspheres. The resulting dispersionwas transferred at a rate of about 120 g/min via fluid delivery system145 into the reservoir 708 of a spinning disk 105 having a diameter ofabout 76.2 mm, rotating at a rate of about 3000-4000 rpm. Themicrospheres were formed by evaporative removal of the solvent with anoutlet temperature of the process chamber 160 of about 45-50° C. A 71%yield (17.9 g) of microcapsules was collected using a cyclone separator.

In the Examples recited above, the spinning disk 105 utilized includedthe substantially flat surface 711 substantially parallel to the diskrotational axis beneath annular surface 706 proximate outer peripheraledge 707, and the teeth 712 disposed on the outer peripheral edge 707.The inclusion of surface 711 having this geometry facilitates theproduction of disks that have lower surface variability and thereforeexhibit decreased wobbling during rotation. A conventional diskfabricated had a substantial horizontal and vertical displacement, whichresulted in measurable “wobble” during rotation, but could be “tuned” toprovide narrow particle size distributions by optimizing parameters suchas fluid flow rate, fluid viscosity, disk rotation speed, and othervariables known to those skilled in the art. However, while conventionaldisk operation could be so optimized, these optimum processingconditions were extremely narrow and processing outside these conditionsresulted in significantly broader particle size distributions. Incomparison, fabricating a conventional disk including a substantiallyflat surface 711 reduced the vertical and horizontal displacement toabout 5-10 μm and the disk exhibited remarkably reduced levels ofvibration during operation. Studies conducted indicate that lowervibrational levels resulted in reduced particle size variabilitycompared to the conventional “wobbling” disk over a broad range ofoperating conditions.

Further studies conducted indicate the same phenomenon occurs with diskshaving the design of spinning disk 105 disclosed herein. A spinning disk105 prepared without inclusion of a substantially flat surface 711 andhaving a disk variability of about 38 μm generally exhibited tighterparticle size distributions than a similar disk 105 fabricated with asubstantially flat surface 711 and having a surface variation of about7.6 μm. However, analogous to the performance observed for theconventional disk, the general variability over a variety of operatingconditions was lower for the spinning disk 105 comprising thesubstantially flat surface 711 than for similar disk 105 fabricatedwithout a substantially flat surface 711. Not to be bound by theory, itis believed that the absence of disk vibration allows for bettercontrolled particle breakup to occur on the disk surface resulting innarrower particle size distributions.

It is known that particle formation at a disk periphery can beinfluenced by the presence of evenly spaced conical tips or cones. See,e.g., Babu, S. R., “Analysis of Drop Formation at Conical Tips,” J.Colloid Interface Sci., 116 [2], 350-372 (1987). The inclusion ofserrations or teeth 712 in spinning disk 105 greatly narrows theparticle size distribution. Studies conducted comparing the particlesize distribution of microparticles produced using a spinning disk 105comprising a substantially flat surface 711, with and without teeth 712,indicate that the particle size distribution for the former isconsiderably narrow than for the latter. While this result is notnecessarily unexpected, what is surprising is the magnitude of thedecrease in particle size variability achieved with the “serrated”spinning disk 105.

For each of the non-serrated spinning disks tested that included asubstantially flat surface 711 or the equivalent thereof, spinning disk105 produced particle distributions that were on average 72% broaderthan particle populations produced by the conventional disk. Theserrated spinning disk 105 produced the narrowest particle sizedistributions, which on average were 58% smaller than particle sizedistributions produced by the conventional disk. FIG. 9 graphicallydisplays particle size distribution curves generated by comparing ahypothetical population of particles having an average diameter of 250μm. As shown by graph 900 in FIG. 9, particles produced by theconventional disk would range in size from about 75 to 1000 μm (curve901), particles produced by the non-serrated spinning disk 105 wouldrange in size from about 25 to 2,500 μm (curve 902), and the particlesfrom the serrated spinning disk 105 would range in size from about 175to 500 μm (curve 903).

Disk wetting is another factor that influences microparticle formation,and therefore studies were conducted to determine the effects thereof onmicroparticle formation. While spinning disk 105 may be fabricated fromany suitable material, the microparticle production examples disclosedherein were carried out using a stainless steel disk. A stainless steeldisk surface is expected to have a high free energy, leading to limitedwetting conditions. A conventional disk surface made of 304 stainlesssteel was initially conditioned by washing it with soapy water, thenrinsing it with water followed by acetone, and finally drying the diskin air at 60° C. for one hour. The disk was then stored under nitrogen.Against this baseline, the disk surface was treated with a variety ofmaterials, including Tergitol™ TMN-100 surfactant (available from DowCorporation, Midland, Mich.), methanol, and water. Contact anglemeasurements were made upon application of various process solutions tothe disk surface and observations were made while fluid was flowedacross the disk surface during rotation of the spinning disk.

The studies indicate that repeatable microparticle formation is morereadily achieved when the fluid flow across the disk surface achievesfull wetting thereof. The results indicate that generally, the liquidsurface tension of the process solution to be atomized on the spinningdisk needs to be less than about 40 dynes/cm to ensure surface wettingof a clean, dry stainless steel disk. Alternatively, the disk surfacefree energy may be reduced by specific adsorption low free energyspecies or by fabricating the disk from intrinsically low free energymaterials.

While reduced particle size variation is one objective of the presentinvention, another objective is the reduction of “pure” shell materialparticles (satellite or placebo particles) produced during microcapsuleformation. One skilled in the art would know that by manipulating theviscosity of the polymer solution used in the overcoating process, onecan reduce the amount of satellite particles produced. However,increasing polymer solution viscosity leads to, at some point,microsphere aggregation (overcoating of multiple microspheres to formone large microcapsule). By using the apparatus of the present inventionto produce microcapsules, lower levels of placebo particles aretypically formed and more uniform, thicker coatings can be applied.Microcapsule formation using a serrated spinning disk 105 comprising asubstantially flat surface 711 can produce microcapsules containingsignificantly decreased levels of satellite particles (FIGS. 10 and 11)as compared to a process using a conventional disk (FIGS. 12 and 13).The reduction in placebo particles translates to an improved yield ofmicrocapsules. In addition, as noted above, a more uniform, thickercoating can be applied using the apparatus of this invention compared toa conventional disk (FIG. 11 versus FIG. 13).

Another advantage of the present invention is reduced particleagglomeration. While as described above the design of spinning disk 105allows for the production of microparticles having a narrow particledistribution, agglomeration of microparticles produced and collectedcauses problems in handling. The design features described above, suchas thermally-controlled and/or low thermal conductivity surfaces, reduceparticle agglomeration.

The apparatus of the present invention may be operated continuously asopposed to normal batch-wise manufacturing of microparticles. Thefollowing is given as an example of a 3-day continuous operation. About400 kg of a 5% polycaprolactone solution in methylene chloride wasprepared in feed vessel 135. To this solution was added 6.67 kg ofanecortave acetate (25% payload), and the resulting dispersion wastransferred at a rate of about 90 g/min via fluid delivery system 145into the reservoir 708 of a spinning disk 105 having a diameter of about76.2 mm, rotating at a rate of 3,000-4,000 rpm. The microspheres wereformed by evaporative removal of the solvent with an outlet temperatureof about 42-45° C. inside the plastic (HDPE) process chamber 160. A 93%yield (24.8 kg) of microspheres was collected as a free-flowing powderusing a cyclone separator.

An additional advantage of the present invention is that microcapsulesproduced thereby exhibit improved active agent release properties. In anembodiment of the present invention, microspheres and microcapsulescontaining anecortave acetate as the active agent were preparedaccording to the methods described herein. The microparticles producedwere sterilized by exposure to gamma radiation, at a dose level of 18-25kGy. To measure the active agent release rates thereof, about 5.0 mg ofthe microparticles was weighed into glass bottles containing about 50 mLof a solution of 5% sodium dodecyl sulfate/phosphate (SDS/PBS) buffersolution. The sample bottles were then placed in a 37° C. shaking waterbath. At various time intervals, 100 μL aliquots were removed foranalysis and an equal volume of 5% SDS/PBS solution was replaced.

As shown graphically in FIG. 14, a high payload (>20 wt.% active agent)microcapsule formulation provides a near zero-order release and areduced burst release compared to the microsphere formulations. In FIG.14, graph 1400 shows the amount of the active agent, anecortave acetate,released from various microparticles produced by the present inventionand maintained in 5% SDS/PBS at 37° C. Curve 1401 shows the releaseprofile of microcapsules (PLGA 75:25 coating covering microspherescomprising glyceride matrix) containing 23.8 wt. % active agent. Curve1402 shows the release profile of microcapsules (PLGA 75:25 coatingcovering microspheres comprising glyceride matrix) containing 23.5 wt. %active agent. Curve 1403 shows the release profile of microspherescomprising PLGA 75:25/PEG (95:5) and containing 23.8 wt. % active agent.Curve 1404 shows the release profile of microspheres comprising PLGA75:25/PEG (95:5) and containing 25.7 wt. % active agent. Curve 1405shows the release profile of microspheres comprising PLGA 50:50/PEG(95:5) and containing 25.8 wt. % active agent. Curve 1406 shows therelease profile of unsterilized microspheres comprising PLGA 50:50/PEG(95:5) and containing 24.6 wt. % active agent. Microcapsules andmicrsopheres containing low payloads may exhibit zero order release,however at payloads above about 15%, especially where the encapsulatedagent is highly soluble in the release medium, microspheres andmicrocapsules typically release most of the active agent very quickly(<1 day). The microcapsules of this invention with >20% active agentload do not show a rapid initial release in vitro, but rather a slowzero order release out to 4 weeks. (See curves 1401 & 1402 in FIG. 14).Control of the release rate is a very important component of theformulation where a rapid initial release could waste the active agent,or worse, be toxic to the recipient.

All patents and publications referenced herein, to the extent notpreviously herein incorporated by reference, are hereby incorporated byreference in their entirety to the extent not inconsistent with thedisclosures in this Application. It will be understood that certain ofthe above-described structures, functions, and operations of theabove-described embodiments are not necessary to practice the presentinvention and are included in the description simply for completeness ofan exemplary embodiment or embodiments. In addition, it will beunderstood that specific structures, functions, and operations set forthin the above-described referenced patents and publications can bepracticed in conjunction with the present invention, but they are notessential to its practice. It is therefore to be understood that theinvention may be practiced otherwise than as specifically describedwithout actually departing from the spirit and scope of the presentinvention as defined by the appended claims.

It is therefore, contemplated that the claims will cover any suchmodifications or embodiments that fall within the true scope of theinvention.

1. A spinning disk apparatus for producing microparticles comprising asubstantially circular spinning disk, wherein the spinning diskcomprises: (A) an inner peripheral edge; (B) an outer peripheral edge;(C) a substantially smooth annular disk surface extending between theinner peripheral edge and the outer peripheral edge, wherein (i) theouter peripheral edge defines a first diameter of the annular disksurface, (ii) the annular disk surface has a second diameter defined bythe area circumscribed by the inner peripheral edge, wherein the areacircumscribed by the inner peripheral edge is disposed substantially ina center portion of the spinning disk, and (iii) the annular disksurface extending between the inner peripheral edge and the outerperipheral edge comprises a substantially flat incline; and (D) areservoir disposed in the area circumscribed by the inner peripheraledge of the annular disk surface, wherein (i) the reservoir comprises atop portion thereof defined by the second diameter, and (ii) thereservoir comprises a cross-sectional area defined by a third diameter,located between the bottom of the reservoir and the top portion of thereservoir, wherein the third diameter is greater than the seconddiameter.
 2. The spinning disk apparatus of claim 1, wherein the firstdiameter of the annular disk surface is between about 10 mm and about300 mm.
 3. The spinning disk apparatus of claim 1, wherein the firstdiameter of the annular disk surface and the second diameter of theannular disk surface are in a ratio between about 300:1 and about 2:1.4. The spinning disk apparatus of claim 1, wherein the third diameterdefining the cross-sectional area of the reservoir and the seconddiameter of the annular disk surface are in a ratio between about 20:1and about 1.05:1.
 5. The spinning disk apparatus of claim 1, wherein thesubstantially flat incline comprises an angle between about 5 degreesand about 45 degrees.
 6. The spinning disk apparatus of claim 5, whereinthe substantially flat incline comprises an angle between about 15degrees and about 30 degrees.
 7. The spinning disk apparatus of claim 1,wherein the outer peripheral edge of the annular disk surface comprisesserrations.
 8. The spinning disk apparatus of claim 7, wherein theserrations have a length between about 0 μm and about 5,000 μm.
 9. Thespinning disk apparatus of claim 8, wherein the serrations have a lengthbetween about 500 μm and about 1,500 μm.
 10. The spinning disk apparatusof claim 7, wherein the serrations define an angle therebetween betweenabout 105 degrees and about 15 degrees.
 11. The spinning disk apparatusof claim 10, wherein the serrations define an angle therebetween betweenabout 65 degrees and about 20 degrees.
 12. The spinning disk apparatusof claim 1, wherein the spinning disk comprises a substantially flatsurface beneath the annular disk surface and proximate the outerperipheral edge thereof, wherein the substantially flat surface lies ina plane that is substantially parallel to the rotational axis of thespinning disk.
 13. The spinning disk apparatus of claim 12, wherein thesubstantially flat surface has a length between about 1 mm and about 10mm.
 14. The spinning disk apparatus of claim 1, wherein the apparatuscomprises a process chamber, wherein the process chamber comprises amaterial selected from the group consisting of a thermally controllablematerial, a low thermal conductivity material, and combinations thereof.15. The spinning disk apparatus of claim 14, wherein the thermallycontrollable material comprises jacketed stainless steel.
 16. Thespinning disk apparatus of claim 14, wherein the low thermalconductivity material comprises plastic.
 17. The spinning disk apparatusof claim 14, wherein the process chamber comprises a cone bottom tank,wherein the cone bottom tank comprises a material selected from thegroup consisting of a thermally controllable material, a low thermalconductivity material, and combinations thereof.
 18. The spinning diskapparatus of claim 17, wherein the thermally controllable materialcomprises jacketed stainless steel.
 19. The spinning disk apparatus ofclaim 17, wherein the low thermal conductivity material comprisesplastic.
 20. The spinning disk apparatus of claim 1, wherein theapparatus comprises a sample collection system comprising a cycloneseparator, wherein the cyclone separator comprises a material selectedfrom the group consisting of a thermally controllable material, a lowthermal conductivity material, and combinations thereof.
 21. Thespinning disk apparatus of claim 20, wherein the thermally controllablematerial comprises jacketed stainless steel.
 22. The spinning diskapparatus of claim 20, wherein the low thermal conductivity materialcomprises plastic.
 23. The spinning disk apparatus of claim 1, whereinthe third diameter of the reservoir is disposed proximate the bottom ofthe reservoir.